Flashlight
A flashlight (in North American English) or torch (in most Commonwealth countries) is a small, portable spotlight. Its function is a beam of light which helps to see. It usually requires batteries.
How it works
A torch, or at least the part that projects the light, will work the same way as a light bulb, because that is all a torch is: a light bulb that you can hold and carry around. However, some torches use LED's, which work slightly differently, and are often more powerful, but give the same effect.
Origin
Hundreds of years ago, people used candles for all indoor light. This was expensive, and once the candle was gone, you would have to buy a new one or be stuck in the dark. When electricity was discovered and the light bulb invented, one particularly clever person came up with the idea of a light bulb that you could take with you, anywhere you wanted to go. Thus, the torch was invented.